1. Field of the Invention
The present invention relates to an optical reproduction apparatus that is used to read information from optical recording media, an optical recording apparatus that is used to write information onto optical recording media, an optical pickup, and a photodetector unit.
2. Description of the Related Art
In recent years, various standards adopting different physical formats have been created for optical recording media. For instance, optical recording media based on different standards have different recording densities. This generates demand for a multi-standard optical reproduction apparatus that can reproduce various types of optical recording media having different physical formats.
A multi-standard optical reproduction apparatus, which reproduces optical recording media having different recording densities, is disclosed by Japanese Laid-Open Patent Application No. H9-180212.
In this conventional optical reproduction apparatus, a photodetector unit for receiving returning light reflected by an optical recording medium includes a plurality of photodetectors to obtain received light signals for a three-beam method and received light signals for a differential phase detection method. Here, each of these methods is used to detect a tracking error signal for driving a tracking servo. The three-beam method is used for low-density optical recording media (conventional CD-ROMs), while the differential phase detection method is used for high-density optical recording media (DVD-ROMs).
The optical reproduction apparatus first receives a user""s specification showing whether an optical recording medium placed therein has a high recording density. If the optical recording medium has a high recording density, the optical reproduction apparatus detects a tracking error signal according to the differential phase detection method. If the optical recording medium has a low recording density, the optical reproduction apparatus detects a tracking error signal according to the three-beam method. The optical reproduction apparatus then drives its tracking servo using the detected tracking error signal.
By selectively using the three-beam method and the differential phase detection method to detect tracking error signals in this manner, the conventional optical reproduction apparatus reproduces both of low-density optical recording media, such as CD-ROMS, and high-density optical recording media, such as DVD-ROMs.
As described above, the conventional optical reproduction apparatus is capable of reproducing optical recording media (such as CD-ROMs and DVD-ROMs) having different recording densities. However, it is difficult for this reproduction apparatus to support other types of optical recording media that have recently become available.
More specifically, because recent optical recording media adopt various physical formats having different track pitches and different track shapes (pit sequences or continuous grooves), it is difficult to reproduce these optical recording media with a single optical reproduction apparatus. As a result, a plurality of optical reproduction apparatuses need to be used to reproduce the different types of optical recording media, which puts an enormous economic burden upon consumers. The same problem applies to optical recording apparatuses.
The first object of the present invention is to provide a photodetector unit that is suitable for the reproduction of or recording onto various types of optical recording media that have different track shapes and different track pitches. The second object of the present invention is to provide an optical pickup that is equipped with the photodetector unit and is capable of reproducing or recording onto various types of optical recording media. The third object of the present invention is to provide an optical reproduction apparatus that is suitable for the reproduction of various types of optical recording media. The fourth object of the present invention is to provide an optical recording apparatus that is suitable for the recording onto various types of optical recording media.
The first object is achieved by a photodetector unit for use with an optical pickup that irradiates an optical recording medium with a laser beam and receives returning light reflected by the optical recording medium, where the optical pickup is constructed to (1) divide the laser beam into a main beam, a preceding sub-beam, and a succeeding sub-beam, (2) direct the main beam, the preceding sub-beam, and the succeeding sub-beam toward the optical recording medium, and (3) divide returning lights of the main beam, the preceding sub-beam, and the succeeding sub-beam respectively into first-fourth main returning lights, first-fourth preceding returning lights, and first-fourth succeeding returning lights, and the photodetector unit includes: first-fourth main photodetectors that respectively receive the first-fourth main returning lights; first-fourth preceding photodetectors that respectively receive the first-fourth preceding returning lights; and first-fourth succeeding photodetectors that respectively receive the first-fourth succeeding returning lights.
This construction allows the photodetector unit to detect at least three types of tracking error signals by combining the received light signals from a plurality of photodetector groups. Therefore, the optical pickup equipped with this photodetector unit appropriately drives the focusing servo and tracking servo according to the tracking error signal corresponding to the type of the optical recording medium.
Here, the first-fourth main photodetectors may be arranged in a virtually straight line, and each of the first-fourth main photodetectors may include at least two photodetecting portions arranged perpendicular to an arrangement direction of the first-fourth main photodetectors. The photodetector unit may further include: a first wiring group that includes first signal lines and transmits a received light signal used to perform a push-pull method, the first signal lines being respectively connected to the photodetecting portions of the first-fourth main photodetectors, the first-fourth preceding photodetectors, and the first-fourth succeeding photodetectors; a second wiring group that includes second signal lines and transmits a received light signal used to perform a differential phase detection method, the second signal lines being respectively connected to the photodetecting portions of the first-fourth main photodetectors; and a third wiring group that includes third signal lines and transmits a received light signal used to perform a three-beam method, the third signal lines being respectively connected to the first-fourth preceding photodetectors and the first-fourth succeeding photodetectors.
With this construction, the first-third wiring groups output received light signals respectively appropriate to the push-pull method, differential phase detection method, and three-beam method that are tracking error signal detection methods.
Here, the photodetector unit may further include: a first circuit that generates a first tracking error signal from the received light signal, which is transmitted from the first wiring group, according to the push-pull method; a second circuit that generates a second tracking error signal from the received light signal, which is transmitted from the second wiring group, according to the differential phase detection method; and a third circuit that generates a third tracking error signal from the received light signal, which is transmitted from the third wiring group, according to the three-beam method.
With this construction, the first-third circuits independently generate the first-third tracking error signals according to the push-pull method, differential phase detection method, and three-beam method.
The first object is also achieved by a photodetector unit for use with an optical pickup that irradiates an optical recording medium with a laser beam and receives returning light reflected by the optical recording medium, where the optical pickup is constructed to (1) divide the laser beam into a main beam, a preceding sub-beam, and a succeeding sub-beam, (2) direct the main beam, the preceding sub-beam, and the succeeding sub-beam toward the optical recording medium, and (3) divide returning lights of the main beam, the preceding sub-beam, and the succeeding sub-beam respectively into first-fourth main returning lights, first-fourth preceding returning lights, and first-fourth succeeding returning lights, and the photodetector unit includes: first-fourth main photodetectors that are arranged in a virtually straight line and respectively receive the first-fourth main returning lights; first-fourth preceding photodetectors that are arranged in a virtually straight line and parallel to an array of the first-fourth main photodetectors on a side of the array, the first-fourth preceding photodetectors respectively receiving the first-fourth preceding returning lights; first-fourth succeeding photodetectors that are arranged in a virtually straight line and parallel to the array of the first-fourth main photodetectors on an opposite side of the array, the first-fourth succeeding photodetectors respectively receiving the first-fourth succeeding returning lights; a current-voltage conversion circuit group that converts current signals, which are obtained from the photodetectors and correspond to received light amounts, into received light signals representing voltage values corresponding to the received light amounts; a first wiring group that transmits a first received light signal group used to perform a push-pull method, the first received light signal group corresponding to photodetecting portions of the first-fourth main photodetectors, the first-fourth preceding photodetectors, and the first-fourth succeeding photodetectors; a second wiring group that transmits a second received light signal group used to perform a differential phase detection method, the second received light signal group corresponding to the photodetecting portions of the first-fourth main photodetectors; and a third wiring group that transmits a third received light signal group used to perform a three-beam method, the third received light signal group corresponding to the first-fourth preceding photodetectors and the first-fourth succeeding photodetectors, where the photodetectors, the current-voltage conversion circuit group, and the wiring groups are integrally formed on a single semiconductor substrate.
With this construction, the optical reproduction apparatus equipped with the present photodetector unit is capable of using a plurality of tracking error signal detection methods by combining the received light signals of the photodetector groups. This allows the optical reproduction apparatus to support various types of optical recording media having different track shapes and different track pitches. Also, because the photodetectors, current-voltage conversion circuit group, and wiring groups are integrally formed on the same semiconductor substrate with a semiconductor processing technique, the photodetector unit is produced with high accuracy and the number of parts and cost of the photodetector unit are reduced.
Here, a second semiconductor laser element may be further provided on the substrate, the second semiconductor laser element emitting a laser beam virtually perpendicular to the surface of the substrate, the first and second semiconductor laser elements emitting laser beams of different wavelengths.
With this construction, the photodetector unit uses two semiconductor laser elements. This allows two types of tracking error signals to be detected according to each tracking error signal detection method. As a result, the number of types of optical recording media supported by the present photodetector unit is increased, and a semiconductor laser element, which emits the laser beam of a wavelength appropriate to the type of the optical recording medium, is selected during recording or reproduction.
The second object stated above is achieved by an optical pickup that irradiates an optical recording medium with a laser beam and receives each returning light reflected by the optical recording medium, including: a first semiconductor laser element that emits the laser beam; a first diffraction grating that divides the laser beam from the first semiconductor laser element into a main beam, a preceding sub-beam, and a succeeding sub-beam; a lens that has the main beam, preceding sub-beam, and the succeeding sub-beam converge on the optical recording medium; a second diffraction grating that is provided virtually parallel to the first diffraction grating and generates first-fourth main returning lights, first-fourth preceding returning lights, and first-fourth succeeding returning lights by dividing each of returning lights of the main beam, the preceding sub-beam, and the succeeding sub-beam into a first half beam and a second half beam and dividing each of the first and second half beams into two beams; and a photodetector unit that includes first-fourth main photodetectors that respectively receive the first-fourth main returning lights, first-fourth preceding photodetectors that respectively receive the first-fourth preceding returning lights, and first-fourth succeeding photodetectors that respectively receive the first-fourth succeeding returning lights, where photodetecting surfaces of the photodetectors are arranged within virtually the same plane, and the photodetector unit is arranged so that the photodetecting surfaces are positioned virtually parallel to the first diffraction grating.
With this construction, the optical reproduction apparatus equipped with this optical pickup is capable of using a plurality of tracking error signal detection methods by combining the received light signals of the photodetector groups. This achieves an optical pickup that supports various types of optical recording media having different track shapes and different track pitches.
The third object stated above is achieved by an optical reproduction apparatus that reads and reproduces information recorded on an optical recording medium by performing tracking servoing for an optical pickup according to a tracking error signal, the optical reproduction apparatus including: a detection unit for detecting first-third tracking error signals according to different methods; a judging unit for judging which one of the first-third tracking error signals is suitable for a tracking servo according to amplitude levels of the first-third tracking error signals detected while the tracking servo is off; and a selection unit for selecting one of the first-third tracking error signals for the tracking servo according to a judgement result of the judging unit.
By combining the received light signals of the photodetector groups of the photodetector unit, this optical reproduction apparatus is capable of using a plurality of tracking error signal detection methods. With the construction stated above, the optical reproduction apparatus selects a tracking error signal detection method, which is appropriate to the type of the optical recording medium. As a result, the optical reproduction apparatus precisely controls the focusing and tracking operations of the optical pickup and reproduces information on the optical recording medium with accuracy.
The fourth object stated above is achieved by an optical recording apparatus that records information onto an optical recording medium by performing tracking servoing for an optical pickup according to a tracking error signal, the optical recording apparatus including: a detection unit for detecting first-third tracking error signals according to different methods; a judging unit for judging which one of the first-third tracking error signals is suitable for a tracking servo according to amplitude levels of the first-third tracking error signals detected while the tracking servo is off; and a selection unit for selecting one of the first-third tracking error signals for the tracking servo according to a judgement result of the judging unit.
By combining the received light signals of the photodetector groups of the photodetector unit, this optical recording apparatus is capable of using a plurality of tracking error signal detection methods. With the construction stated above, the optical recording apparatus is capable of selecting a tracking error signal detection method, which is appropriate to the type of the optical recording medium. As a result, the optical recording apparatus precisely controls the focusing and tracking operations of the optical pickup and records information onto the optical recording medium with accuracy.